1. Field of the Invention
The present invention relates an electronic part, an electronic part mounting element and a process for manufacturing such the articles.
2. Description of the Related Art
There is recently a growing acknowledgment on the environmental problem and therefore regulations by laws are being imposed on the lead in the solder alloy in the field of electronics mounting. Therefore, it is an urgent necessity to establish the joining technology which does not use lead for mounting of the electronic part. As the mounting technology which does not use lead, the technology which utilizes a lead-free solder and that which utilizes a conductive adhesive are mainly given. Among them, the mounting structure which utilizes a conductive adhesive draws the attention because the advantage of the flexibility of the joining part, lowering the temperature of mounting and the like is expected.
A conductive adhesive is generally configured by dispersing a conductive filler in the adhesion ingredient based on resin. The conductive adhesive layer electrically connects an external electrode of an electronic part to a connecting terminal of a circuit board by curing a resin ingredient of the conductive adhesive layer after the conductive adhesive layer is interposed between the electronic part and the circuit board. Then, conduction of electricity of a connecting portion is ensured through a contact among the conductive fillers. Because said connecting portion adhered through resin, the conductive adhesive is flexible for a deformation due to heat and external forces and resistant to cracking in the connecting portion compared with solder in which said connecting portion is an alloy. Further, the conductive adhesive may be cured at a lower temperature than that in solder. From such a reason, the conductive adhesive is expected as an alternative material to solder.
However, when the current conductive adhesive is used in mounting the electronic part having a solder-plating electrode generally supplied at present to the circuit board, it is sometimes difficult to use it for actual applications since sufficient adhesion strength and reliability may not be attained.
And, an electronic part having a tin-plating electrode also is supplied as a mounting structure of lead-free permeates. However, in a structure mounted by the conductive adhesive upon the tin-plating electrode, adhesion strength and reliability is considerably low compared with the conventional soldered connection.
As described above, when the electronic part having a metal electrode represented with a solder-plating electrode and a tin-plating electrode is intended to mount to the circuit board by using the conductive adhesive, sufficient adhesion strength and reliability may not be attained sometimes.
This results from that the external electrode of the electronic part supplied at present is designed to suit with the soldered connection and it is necessary to change the external electrode of the electronic part to the specifications suitable for a connection by the conductive adhesive.
Further, the destruction due to detachment in a mounting structure using the conductive adhesive occurs at the contacting interface between the conductive adhesive and the electrode. Most of the surfaces of the external electrodes (applied with solder plating or tin plating) of the electronic parts supplied at present are smoothed to suit with the soldered connection. Therefore, connecting strength at the contacting interface where the destruction due to detachment occurs may not be sufficiently retained and this causes that adhesion strength may not be sufficiently attained.